The invention relates generally to devices for simplifying the filling and maintenance of fluids in battery cells and more particularly to an automatic fluid filling device for maintaining fluid at a desired level in conventional lead acid batteries. Prior fluid filling devices are disclosed in Beall U.S. Pat. No. 3,318,345, issued May 9, 1967, Lowe U.S. Pat. No. 3,189,063, issued June 15, 1965, Droste U.s. Pat No. 2,645,907, issued July 23, 1953, Heckendorf U.S. Pat. No. 2,670,889, issued Mar. 2, 1954, Harstick U.S. Pat. No. 2,668,001, issued Feb. 2, 1954, and Duncan U.S. Pat. No. Re. 23,543, reissued Sept. 2, 1952.